There are several possibilities here. I think the fact that the swelling is better is an excellent sign, although the persistent pain should probably be evaluated. You could talk to your primary care doctor
about the issue, especially if the symptoms persist. They can examine your foot for any signs of a serious problem.
The most common cause of bumps on the bottom of the foot would include a callus, caused by friction of the skin from tight shoes or some similar trauma. A callus can periodically be very painful, especially if you put a great deal of pressure on it (say, from standing on your feet all day long). This could lead to some mild swelling and redness, which would likely subside over night as you rested. Similarly, a plantar wart on the sole of the foot could cause a reddened, painful, or swollen lump on the bottom of the foot, which could likewise periodically swell more and be more noticeable.
Both of these problems can be treated in part by wearing comfortable, well fitting shoes. Additionally, however, they sometimes require shaving, freezing, or other treatments to relieve the pressure, and this is something either your podiatrist
or primary care doctor can help with. Please speak with them soon!